In the health care field, it is becoming increasingly common to use disposable pumping cassettes for pumping medical solutions. The cassettes are made of plastic and are operated by non-disposable driver mechanisms external to the cassette. Disposable cassette pumps offer many advantages over pumps with permanent pumping chambers. For example, disposable cassette pumps can be easily set up and readily changed over from prior pumping procedures without the need for sterilizing the permanent pump apparatus. Further, the disposable cassette pump apparatus allows for regular changing of the pumping pathway to reduce the risk of contamination without taking the pump equipment out of use for the period of time needed to sterilize the equipment.
Monitoring the pressure of the fluid being pumped through the cassette can provide useful information for controlling the pump. As disclosed in U.S. Pat. No. 4,457,753 monitoring cassette pressure permits the detection of occlusions or plugged filters in the cassette outlet line leading to a patient, for example. As disclosed in U.S. Pat. No. 4,842,584 monitoring cassette pressure also permits the valves to be checked for leakage. Further, when used as an infusion system, monitoring the discharge pressure of the cassette can be used to determine the patient's blood pressure.
U.S. Pat. No. 4,950,244 to Fellingham et al, hereby incorporated by reference, discloses a pressure transducer which can detect occlusions in the cassette inlet line from the solution container to the cassette.
However, while the above described pressure monitors are accurate, they are very complex and various parameters associated with the cassette must be strictly controlled. The need to control the parameters reduces the flexibility that the pumping apparatus can be used in and creates the potential for inaccurate results if the pump is used outside the controlled range of parameters. Thus there is a need for a simplified pressure sensor than can make accurate pressure measurements without the need for strict control of certain parameters.